In a case that a pixel shape in a luma domain is not similar to a pixel shape in a chroma domain in an input image, a prediction image that is generated in the reuse of a luma prediction mode is made more accurate.A moving image decoding apparatus 1 includes a gradient deriving unit 1453B that references a chroma gradient definition DEFANG1C, and derives a chroma prediction direction from a prediction mode based on a luma prediction direction.
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1. An image decoding apparatus configured to reconstruct an image from coded data by generating prediction images in terms of luma and chroma through intra-prediction method corresponding to a prediction mode respectively, the image decoding apparatus comprising: a chroma prediction circuit that corrects a prediction direction in a case that chroma prediction image generation is performed in accordance with the prediction mode used in luma prediction image generation with a color format of the image being a 4:2:2 format, wherein the chroma prediction circuit corrects a first prediction mode for use in the luma prediction image generation to a second prediction mode for use in the chroma prediction image generation by referencing a prediction mode conversion table to convert the first prediction mode, wherein the prediction mode conversion table is a table that results in the first prediction mode in luma space and the second prediction mode in chroma space having approximately a same gradient of prediction direction in a coordinate system.
2. An image decoding method for reconstructing an image from coded data by generating prediction images in terms of luma and chroma through an intra-prediction method corresponding to a prediction mode respectively, the image decoding method comprising: correcting a prediction direction in a case that chroma prediction image generation is performed in accordance with the prediction mode used in luma prediction image generation with a color format of the image being a 4:2:2 format, wherein a first prediction mode for use in the luma prediction image generation is corrected to a second prediction mode for use in the chroma prediction image generation by referencing a prediction mode conversion table to convert the first prediction mode, wherein the prediction mode conversion table is a table that results in the first prediction mode in luma space and the second prediction mode in chroma space having approximately a same gradient of prediction direction in a coordinate system.
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January 24, 2013
March 29, 2016
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